Revision as of 15:09, 4 January 2017

OxHack's laser cutter is a Just Add Sharks Silvertail A0.

OxHack's Just Add Sharks Silvertail A0 laser cutter

It cuts 2-dimensional shapes from many different materials, up to A0 in size (841 x 1189mm), by burning through them with an 80 watt laser. Its software accepts DXF files, which can be exported from many popular CAD and graphic design packages.

Quick guide to the rules

Hackspace members

• Don't operate the laser cutter unless you've been trained
• Stick to the approved materials list
• Always use the filtration system
• Always use the compressed air supply except in very special circumstances (see ventilation system section)
• Never leave the machine working unattended
• If in doubt, ask
• If something goes wrong, tell!

Prototyping service customers

Please see the Laser Cutting Job Guidelines for details on how to submit a job to OxHack.

Laser cutter anatomy

Components

• Laser cutter
• Chiller - beige box with an LED temperature readout on the front. This supplies cooling water to the laser tube.
• Compressor - small metallic device behind the cutter, pumps compressed air to the laser head
• Filtration system - large steel box on top of the blue racking
• Blower - powerful fan that draws air through the cutter and filtration system
• Laptop - runs the software that powers the cutter

Layout

The 80W water-cooled laser tube is at the back of the laser cutter. It's around a metre in length, and points towards the left-hand side of the machine. The laser beam it produces is a few mm in diameter, and bounces off a series of mirrors on its journey to the cutting head. The last of these mirrors move with the gantry that supports the cutting head. The mirrors are adjustable, to ensure the beam arrives at exactly the right spot regardless of the location of the cutting head. After the final mirror, the beam is pointing downward, it passes through a lens, which focusses it on the workpiece, in a concentrated spot a fraction of a millimetre across. The focus is dependent on the distance to the workpiece, so the cutting bed is height-adjustable to cope with different thicknesses of material.

The laser cutter

The cutter itself has a display and control panel on the right, and the door opens upward to reveal the cutting bed. Opening the door disables only the laser beam, and will not prevent the cutting head from moving. Inside, the following components are found:

Hex bed

Inside the laser cutter, the hex bed supports the workpiece. It is unaffected by brief contact with the laser beam, and its geometry allows much of the energy to shine through it, along with the debris and smoke from the cut surfaces. It should be supported by the knife bed to allow proper ventillation, and not placed directly on the flat bed. It is not fixed in place, and can be removed if necessary.

Knife bed

The knife bed sits below the hex bed, and provides a level surface to support it, whilst allowing air to flow freely, carrying away smoke and debris. It is made of aluminium, and is good at dissipating energy from the laser beam.

Flat bed

The final layer of the cutting bed is a solid aluminium base, which provides a solid surface and dissipates any remaining energy from the laser.

X-Y gantry

This is the structure that supports the optical components that direct the laser beam onto the workpiece. It's heavy, and moves fast, and is not interlocked with the main door, so take care around it.

Cutting head

The cutting head focussed the laser beam onto the workpiece. It is connected to the compressed air supply, which helps blast debris away from the workpiece and lens. It incorporates a sighting laser, which projects a red dot onto the workpiece at the location of the laser focal point, when the Z-height is set correctly.

Chiller

The chiller sits on the floor to the left of the laser cutter, and pumps water through the laser tube to keep it cool. It is powered directly from the laser cutter, so it should be impossible to run the cutter without it being switched on. If the flow of water is interrupted, an alarm will sound, and the laser will be prevented from powering up.

Laptop

The laptop runs LaserCut, the software that operates the laser cutter. It has a USB security dongle that is required for the software to work, and it connected to the cutter via a USB cable. The laptop is intended solely for running the laser cutter, rather than for design work.

Fume extraction system

Filtration system

The laser cutter cuts materials by burning through them with a powerful laser. This creates unpleasant smoke, ash and fumes, which are extracted and handled by a 4-stage filtration system. A large blower located at the exit of the filter housing pulls air through the filtration system, creating a negative pressure throughout, to avoid any pollutants leaking into the room. Air enters the laser cutter, through a hole in the lower half of its rear panel. It passes under the cutting table, then flows around its edges, flowing over the work towards the extraction grille at the back.

Compressed air system

A small air compressor feeds air to the cutting head, where it blows out of the nozzle onto the workpiece. One purpose of this arrangement is to blast ash and debris from the surfaces as they are cut by the laser, giving a cleaner finish and better penetration of the laser beam. The other is to stop soot and gunge building up on the laser lens, which could cause it to overheat and become damaged.

The only reason the compressed air supply may not be appropriate, is when you're cutting something extremely light or fragile, which would be disrupted by the flow of air from the nozzle. Keep in mind, even if small, light parts become detached from the workpiece during cutting, they tend to get pushed away from the laser head by the compressed airflow, and rarely get in the way of the laser beam.

Optimisations

We have sealed some of the gaps in the machine, to help air flow through it in the best way to carry away pollutants. There's still some room for improvement and experimentation. The most notable problem is that when the cutting head is near the front of the machine, the compressed air flowing through the nozzle can push dirty air out of the gaps around the door. Any contributions towards making the cutter handle airflow better are welcome.

Operation

Do not attempt use the laser cutter without being trained.

Safety

Fire

Using lasers to cut flammable materials carries an inherent risk of fire. For this reason, the following rules must always be followed:

• Be aware of the location of the nearest fire extinguisher. Currently, this is just outside the door of the laser cutter room. Only use CO2 extinguishers on the laser cutter.
• Never leave the laser cutter unattended while cutting.
• If you see flames on the material you are cutting, watch for a few seconds to see if they self-extinguish. If not, fetch the fire extinguisher.
• Record any sustained fire incidents in the Laser Cutter Fire Incident Log. This will help us improve our safety policies.

Most importantly, do not put yourself at risk. If you are unable to deal with a fire, sound the alarm and leave the building.

Eye safety

The CO2 laser in the cutter emits at a wavelength of 10.6 μm, in the invisible infra-red band. It is very powerful, and has the potential to cause retinal burns if it enters the eye, even as a reflection. The glass lid of the laser cutter absorbs infrared, to protect the user from any rays shining outward from the cutting bed. There are some gaps around the lid, through which IR rays could possibly escape. Internal baffles are planned to seal these gaps, but until they are fitted, as a precaution, do not bend down to the height of the cutting bed when the cutter is in use.

While cutting materials the laser can produce a bright spot in the cutting zone. Like any bright light, it's advisable not to look directly at this spot.

Fumes

The extraction system is very effective, and draws polluted air from the cutter through several stages of filtration, and then outside the building. Always use it while cutting. If you notice any strong and unpleasant fumes while cutting, check the extraction system is working properly. After cutting has finished, wait for a minute or so before opening the cutter lid, to allow smoke and fumes to clear.

Types of operation

The laser cutter is capable of two primary modes of operation; engraving and cutting. Their names are slightly misleading, so please read the descriptions below.

Cutting

Cutting describes a laser operation where the laser follows a vector path at a given speed and power. This is useful to cut materials, but at reduced power or increased speed, it can also be used to engrave the surface of materials with fine lines.

Engraving

In laser cutter terminology, engraving doesn't simply mean to mark the surface of a material; it describes a laser operation in which the laser scans repeatedly across the workpiece like a printer, while the laser power is modulated to mark the surface in a given pattern. Increasing the laser power or reducing the scanning speed will cause more of the surface to be vaporised, so 'engraving' operations can reach substantial depths into a workpiece, or cut through it entirely. Engraving can use closed vector paths as a source, or a bitmap. However, bitmaps undergo a threshold conversion to 1-bit, so greyscales are not reproduced.

Other modes

The Lacercut software provides two extra functions; 'GradeEngrave' and 'Hole'. These are rarely useful, but further information about them can be found in the Just Add Sharks support articles.

Software

The first step is to create a DXF file, using a 2D drawing package of your choice. It can then be imported into Lasercut, the software that controls the cutter.

Packages to use

Lasercut accepts DXF files, which can be created using many drawing and graphics packages. Some free ones we recommend:

• LibreCAD - slightly clunky, but adequate for dimensionally accurate mechanical drawings
• Inkscape - more suited to creative and graphic design work (When using shapes, use " Path > Convert object to path" and then select "Extensions > Modify Path > Flatten Beziers". The laser cutter software does not accept bezier curves.To export select Save as: Desktop Cutting Plotter (.dxf))

Lasercut notes

Designing for Lasercut

For a smooth transition from your drawing package to Lasercut, pay attention to the following:

• Lasercut is not user-friendly. To save headaches, do as much of the layout and design of your job as you can in your own software, before importing. Don't save any lines in your file that you don't want to cut.
• DXF files don't necessarily can contain information about scale and units. For parts to be the right size when imported, make sure your chosen package saves your files in millimetres.
• DXF files support layers, but they are ignored by Lasercut. Only colours are differentiated, and these are approximated to the nearest colour in Lasercut's palette.
• If you want to use multiple cutting parameters in the same job, differentiate them using colours; one colour for one set of cutting parameters.
• Be aware of any repeated lines in your design; i.e. multiple identical lines occupying the same space. They will be cut multiple times by Lasercut, which can lead to unpredictable results.
• Text does not import well into Lasercut. Many design packages have an 'explode' feature to deconstruct text into its constituent lines. Use this for all text before saving to DXF.

Importing into Lasercut

The Lasercut software shows a representation of the A0 cutting bed. DXF files can be imported and edited to achieve the right results.

After importing, select the 'unite lines' option on the 'Tools' menu and click 'Apply'. This will join adjacent lines in your design together, allowing the cutter to cut them more efficiently.

Saving files

If you want to save the cutting parameters you have set up for a job, you will need to save your work in Lasercut. It's important to note that when it saves drawings as '.ecp' files, it simultaneously creates a number of extra files with different extensions. One of these, the '.ini' file, is particularly important, since it contains the cutting parameters assigned to each colour in the drawing. When moving files off the laser cutter laptop, take care to copy every file necessary.

Lasercut quirks

Lasercut displays colours in the layer list in the order that they were first selected in a new file. No amount of tinkering with an existing file will change the order, which can be problematic when trying to keep track of numerous layers, for example in a parameter test file. Be careful to select colours in an imported drawing in the order you want them to be displayed.

Cutting parameters

The two important parameters governing how the laser cutter cuts material are the laser power and feed rate. They can be set independently in the Lasercut software. A guide to cutting parameters for whitelisted materials can be found on the Laser Cutter Materials List wiki page.

Laser power

A graph showing how laser output varies with input current

The cutter's laser produces powerful infrared laser light. The intensity of the laser dictates how much power is delivered to the workpiece. More power generally allows faster cutting, or cutting of thicker materials.

The current being fed to the laser can be seen on the needle dial above the machine's control panel. Although laser output power does not vary linearly with current input (see graph on the right), the laser cutter and its software have been set up to operate within the safe power range of the laser (the lower portion of the graph), so the full 0-100% range is available and safe to use.

The laser cutter bed is designed to dissipate the laser energy being fired at it, so there are no adverse consequences to firing the laser at 100% power into the cutting bed. However, too much power can cause reflections that scorch the underside of the material, or cause unnecessary melting. Experiment or follow advice to achieve the cleanest cut you can.

Cutting speed

Cutting speed is defined in mms^-1. The slower the cutting speed, the more power is delivered to make a cut. Reducing cutting speed has a similar effect to increasing laser power. However, setting the cutting speed too low can increase the risk of your workpiece catching fire.

Materials

Only whitelisted materials are permitted on the cutter. Cutting parameters are recommended for each material. These are guidelines, and you may find other parameters yield better results. Please record any useful discoveries in the wiki.

If you wish to cut a material not yet on the whitelist please first contact one of the laser cutter trainers.

The materials whitelist and a guide to cutting parameters can be found on the Laser Cutter Materials List wiki page.

Troubleshooting

This is a list of problems we've observed, and how to fix / work around them.

Failure to reset datum on startup

On starting up, the machine usually moves the laser head to the rear right-hand corner of the cutting bed, where it hits the X and Y limit switches that set its datum location. If the machine doesn't do this, it's liable to crash into the hard limits of its X-Y travel, because it doesn't know where those limits are. You can manually ask the machine to reset its datum by pressing the 'datum' button.

The problem can be cured permanently by using the method below, under 'Resetting the configuration to the default settings'.

Strange datum behaviour

'Logic Org' mode is used to save an origin point and reload it when the machine is turned back on. It's easy to set accidentally by pressing 'enter' on the control panel too many times. To turn it off:

• Press 'enter' to change menus until the option 'CANCEL LOGIC ORG' appears
• Select it and press 'enter' again.

Design cuts erratically

If the cutter jumps around erratically rather than cutting your design in the most efficient way, check that you united the lines in your design after importing, as described above.

Laser head moves to a specific location for preview

This can be a result of 'Immediate' being ticked in the download window, when the file is uploaded to the cutter. Untick the box, re-upload the file, and try again.

Resetting the configuration to the default settings

Follow these steps to reset and re-upload the configuration settings to the cutter:

• Close LaserCut
• Locate LaserCut's directory on the laptop
• Run 'silvertail.bat'. This overwrites LaserCut's config file (config.ini) with the defaults for the Silvertail cutter.
• Click the 'DownLoad' button
• Click 'Download CFG' to upload the default settings to the cutter.

Laser cutter trainers

Paul Riggs (Technician)

Jared Reabow (Technician)

Useful external links

Just Add Sharks support articles

Gallery

How it got here

Further information

The Laser Cutter was received by the Hackspace on December 4th 2015.